In my opinion, you have as much right to fire them as they do for you. Sometimes an immediate termination is the right decision, especially if the situation is

In my opinion, you have as much right to fire them as they do for you. Sometimes an immediate termination is the right decision, especially if the situation is an on-going cost on your mental well-being. You can just walk away, if that's what you need to do. As others have noted, there are financial, legal, perhaps moral and reputational aspects to consider. If the estimate of total "loss" you may incur is less than what it costs you to stay, well, you owe it to yourself to fire them. Speculatively, one gets to burn bridges like this only a handful of times in their life/career, even if it's for a reasonable cause. It would be ideal if you can do it "politely", as in, give the minimum required notice (2 weeks?). That would remove/reduce any guilt you may feel about the decision.